The ease and economics of fabricating gears, cams, bearings, sildes, ratchets, and the like with injection moldable thermoplastic resins has led to widespread displacement of metals for these applications. In addition to the inherent processing advantages parts made from these thermoplastic materials have the ability to dampen shock and vibration, reduce part weight, run with less power, provide corrosion resistance, and run quietly. Polycarbonate resins, because of their many excellent physical and mechanical properties such as, for example, toughness, flexibility, impact strength, and high heat resistance, are particularly well suited for this purpose. However, polycarbonate resin parts, akin to other thermoplastic resin parts, are subject to greater wear than comparable metal parts when brought into repeated contact with other moving parts fabricated from metal or other thermoplastics.
It would thus be very advantageous if a polycarbonate composition could be provided which, when fabricated into mechanical moving parts, exhibits substantially most of the advantageous propeties of conventional neat polycarbonates and also exhibits improved wear resistance.
Attempts have been made to improve the wear resistance of polycarbonate resins by blending them with various other resins. These attempts have generally not met with unqualified success. This is due to the fact that in order to provide useful polycarbonate blends exhibiting improved wear resistance the material admixed with the polycarbonate resin must not only improve the wear resistance of the polycarbonate resin but must also be compatible with the polycarbonate, i.e., must not adversely affect the properties of the polycarbonate, and must be combinable with the polycarbonate resin in amounts which are effective to improve the wear resistance properties of the aromatic polycarbonate resin.
Thus, for example, while some materials are both compatible with polycarbonate resins and are combinable therewith over a wide range of concentrations they do not positively upgrade the wear resistance of these resins. Indeed, some of these materials adversely affect the wear resistance of polycarbonates. Other materials, while improving the wear resistance of polycarbonates, are not compatible with polycarbonates or are not combinable therewith in amounts which are effective to improve the wear resistance thereof. Still other materials, while being compatible with polycarbonates and combinable therewith over wide concentrations, need to be present in such large amounts in order to positively upgrade the wear resistance of the polycarbonate that they materially change the character of the polycarbonate resin compositions.
Thus, in order to provide a useful polycarbonate composition exhibiting improved wear resistance not only is the nature of the additive material itself critical, but its concentration in the blends is also of great import.
Furthermore, the degree of effectiveness as a wear improving agent varies widely among the materials which are compatible with polycarbonate resins, are combinable therewith in amounts which are effective to positively upgrade the wear resistance of polycarbonate resins, and which positively upgrade or improve the wear resistance of the polycarbonate resins. That is to say, some materials are more effective in positively upgrading the wear resistance of aromatic polycarbonate resins than other materials when admixed with the polycarbonate resin in substantially identical amounts.
There does not appear to be any great degree of predictability or certainty as to how a particular material will function, as regards its ability to improve the wear resistance of polycarbonate resins, when said material is admixed with polycarbonate resins. The empirical approach is thus generally the rule rather than the exception in the area of improving the wear resistance of polycarbonate resins.
SUMMARY OF THE INVENTION
The instant invention is directed to aromatic carbonate resin compositions exhibiting improved wear resistance. More particularly, it is directed to polycarbonate compositions comprising, in physical admixture, (i) at least one aromatic polycarbonate resin, (ii) at least one polyolefin, (iii) at least one fluorinated polyolefin, and (iv) at least one silicone fluid. The polycarbonate resin is present in a major amount while components (ii)-(iv) are present in amounts effective to improve the wear resistance of said polycarbonate resin.